Power systems such as electrical power distribution or transmission systems are used to supply, transmit and use electric power. High Voltage Direct Current (HVDC) power transmission is becoming increasingly important due to increasing need for power supply or delivery, interconnected power transmission and distribution systems and long transmission distances from generation stations to load centers.
An HVDC converter station is a type of station configured to convert high voltage direct current (DC) to alternating current (AC) or the reverse. An HVDC converter station may comprise a plurality of elements such as the converter itself (or a plurality of converters connected in series or in parallel), an alternating current switch gear, transformers, capacitors, filters, a direct current switch gear and/or other auxiliary elements. Electronic converters may comprise a plurality of solid-state based devices such as semiconductor devices and may be categorized as line-commutated converters, using e.g. thyristors as switches, or voltage source converters, using transistors such as insulated gate bipolar transistors (IGBTs) as switches (or switching devices). A plurality of solid-state semiconductor devices such as thyristors or IGBTs may be connected together, for instance in series, to form a building block, or cell, of an HVDC converter, which may also be referred to as an HVDC converter valve. According to one example, a plurality of solid-state semiconductor devices such as thyristors or IGBTs may be connected in series in a cell of an HVDC converter. During normal operation of e.g. an HVDC power transmission system or an HVDC grid including the HVDC converter, the solid-state semiconductor devices in the HVDC converter may at times be in a conducting mode in which they are conducting current and at other times be in a blocking mode, in order to attain a desired or required wave form of the current, as known in the art.
Components in a power system such as a HVDC power system operating at relatively high DC voltages may be electromagnetically shielded in order to reduce or eliminate the risk of partial discharges, arcing or flashovers occurring between the component and for example a wall, floor or ceiling within a building in which the component is arranged. For example, an HVDC converter is often arranged in a purpose-built building, which may be referred to as a valve hall or converter hall, for accommodating the HVDC converter. The required air clearance between the component and for example a wall, floor or ceiling within a building in which the component is arranged may at least in part depend on the electromagnetic shielding capacity or capabilities of the electromagnetic shield and/or the required or intended operating voltage of the power system.